Automated Quantitative Enzyme Biosensing in 24-Well Microplates.

We report a novel system for glucose estimation in model and real samples, utilizing enzyme-modified pencil leads (PL) as effective electrochemical biosensors for robotic substrate quantification in 24-well microplates. Electrochemically formed carboxyl groups on the surface of the graphite were cross-linked to amino groups in the enzyme so as to attach glucose oxidase to the PL surface. Automated amperometric sensing of glucose solutions in microtiter-plate wells used computer-controlled stepper motors to move the biosensor/counter/reference electrode assemblies sequentially between the samples. This setup achieved stable analyte response and, in calibration trials, a linear response range and detection limit of 0.1-8 mM and 0.05 ± 0.01 mM, respectively. The biosensor microplate assay offered accurate "hands-off" evaluation of 4 or 20 samples per plate run, in the standard addition or calibration curve mode, respectively. Mode-independent glucose assays in standard solutions and human serum samples worked reproducibly with close to 100% recovery. The choice of cheap and practical PL enzyme biosensors and simple nonmicrofluidic measurement automation offers a convenient, labor- and cost-efficient form of quantitative biosensing, with a reduced risk of operator errors. The robotic approach is best suited to repetitive measurements of sample series, with academic research and clinical, environmental, pharmaceutical, or biotechnological analysis being potential areas for future exploitations of the methodology.